With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to above 540 Mbps, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate. The power save mode is supported for power saving of an STA which does not require the active state to receive the frame. An STA supporting the power save mode (PSM) can avoid unnecessary power consumption by operating in a doze mode when it is not a time duration in which the STA can access to its radio medium. That is, the STA operates in the awake state only for a time duration in which a frame can be transmitted to the STA or a time duration in which the STA can transmit the frame. For this, an access point (AP) composing a Basic Service Set (BSS) provides non-AP STAs associated with the AP and/or which located in a BSS service area (BSA) with information about a PSM operation. Therefore, STAs supporting the PSM can transmit and receive frame by switching an operation mode between a sleep mode and an awake mode based on the corresponding information.
With the widespread use of the WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing rate supported by the IEEE 802.11n. A next-generation WLAN system supporting a very high throughput (VHT) is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing rate of above 1 Gbps in a MAC service access point (SAP).
A next-generation WLAN system supporting supports a Multi User-Multiple Input Multiple Output (MU-MIMO) transmission which a plurality of STAs simultaneously access a channel for efficiently using a wireless channel. By using the MU-MIMO transmission, an AP can simultaneously transmit frames to one or more non-AP STA which is MIMO pared to the AP.
Meanwhile, although the AP provides information for operating the PSM mode to the non-AP STA in the conventional WLAN system, an aspect to be considered for MU-MIMO has not been adopted. Therefore, there is a need to discuss on a method for supporting a PSM mode operation of one or more non-AP STAs in a next-generation WLAN system supporting MU-MIMO transmission.